1. Field of the Invention
This invention relates to a communication control device having a transmitting section for serially transmitting two or more input signals, e.g., parallel input control signals, to a controlled section.
2. Description of the Related Art
Various communication control devices are known which allow for communication between units over a communication line. The known communication control devices have more or less the functions as illustrated in block diagram in FIG. 10 hereof.
The illustrated communication control device 100 comprises a controlling section 110, a transmitting section 120, a serial transmission line 130, a receiving section 140, and a controlled section 150.
Based on various inputs, the controlling section 110 supplies a plurality of control signals to a plurality of output ports (0 to N) for controlling the action of the controlled section 150. The control signals supplied to the output ports contain information for controlling a plurality of controlled objects not shown but provided in the controlled section 150.
More specifically, the controlling section 110 outputs, for example, to a first output port a signal instructing a first one of the controlled objects to perform an ON/OFF operation, to a second output port a signal instructing a second one of the controlled objects to perform an ON/OFF operation, to third and fourth output ports signals instructing a third one of the controlled objects to hold four different kinds of operational conditions, and to other output ports values for controlling other controlled objects.
The transmitting section 120 constantly monitors the state of the control signals output from the output ports of the controlling section 110. When a change whatsoever arises in an output state of any one of the output ports, the transmitting section 120 latches the outputs from all of the output ports, parallel-serial converts the latched outputs (into serial bit signals) and supplies the converted signals to the serial transmission line 130 at a preset data transmission speed.
When a change arises in an output state of any output port during an idle state (communication standby state) in which the transmitting section 120 is sending out no serial signals, the transmitting section 120 immediately latches the state of the output port and sends out serial signals.
When a change arises in an output state of any output port while the transmitting section 120 is sending out serial signals, the transmitting section 120 latches the state of the output port and sends out serial signals after transmission of the serial signals being sent out is finished.
The receiving section 140 receives the serially transmitted states of all of the output ports and transmits control signals, resulted from serial-parallel conversion of the received states, to the controlled section 150 in parallel. The states of the output ports of the controlling section 110 are transferred to the controlled section 150 in this manner.
Based on the control signals supplied from the receiving section 140, the controlled section 150 controls the operation of the controlled objects therein.
In the communication control device 100 of FIG. 10, the state of the output ports of the controlling section 110 can be transmitted to the controlled section 150 over a single transmission line connected therebetween.
However, in the above arrangement in which the state of the output ports of the controlling section 110 is transmitted through serial communication to the controlled section 150, there arises a delay corresponding to the time T required for at least the serial communication beginning at the time when a control signal is newly output from the controlling section 110 and ending at the time when the new signal is transmitted to the controlled section 150.
Assume, for example, that the controlling section 110 comprises an electronic control unit (ECU) for the ignition spark control and fuel injection, and that the controlled section 150 comprises an electronic ignition system and a fuel injector. Although the controlling section 110 outputs an ignition control signal in such a manner as to achieve the target ignition timing, the actual ignition occurring at the controlled section 150 is retarded by at least the time T required for the serial communication of the ignition control signal between the controlling section 110 and the controlled section 150.
Thus, the conventional communication control device 100 is arranged so that it outputs control signals intolerable of a delay of the time required for the serial communication, earlier than the target ignition timing (point) set at the controlling section 110 by the time required for the serial communication of the control signals.
Reference is now made to FIG. 11 which illustrates the operation of the conventional communication control device.
Based on input signals from, e.g., a crankshaft position sensor (not shown), the controlling section 110 calculates a rotational speed and angle of a crankshaft as well as a target ignition timing. As shown in (a) of FIG. 11, the controlling section 110 outputs to a predetermined output port an ignition control signal earlier by the time T required for the serial communication than the target ignition point (delay correction).
When it detects a change from a low level to a high level of an ignition control signal as shown in (a) of FIG. 11, the transmitting section 120 latches the output states of all of the output ports and serially transmits the latched state of each output port. Since the data length and data transmission rate is preset, the communication time T shown in (b) of FIG. 11 is constant.
The receiving section 140 receives a series of data sent out from the transmitting section 120, serial-parallel converts the serial signals and outputs the converted signals.
Consequently, after a lapse of the communication time T from the time of output of an ignition control signal by the controlling section 110, an ignition output corresponding to the ignition control signal is supplied from the receiving section 140 to the controlled section 150, as shown in (c) of FIG. 11, thereby effecting the ignition spark at the target ignition point.
Reference is next made to FIG. 12 which is a time chart for explaining the problems of the conventional communication control device.
With the time T required for the serial communication taken into consideration, the controlling section 110 outputs an ignition control signal the time T earlier than the target ignition point (timing). When, prior to the time of output of an ignition control signal as shown in (a) of FIG. 12, a separate or another control signal is output as shown in (b) of FIG. 12 (when there arises a change in the state of an output port), the transmitting section 120 detects a change in the state of the separate control signal and commences serial communication.
Thus, although a control instruction for initiating the feeding of an ignition control signal is output during the serial communication based on a change in the separate control signal, transmission of the state of a new output port including the ignition control signal may not be started until after the previous serial communication is finished (see (c) of FIG. 12).
Consequently, the actual ignition at the controlled section 150 with an ignition output supplied thereto will be delayed with respect to the target ignition point (timing). The maximum value of the time of delay from the target ignition point is equal to the communication time T required for the serial communication.
As is apparent from the foregoing discussion, in the conventional communication control device 100, there will be a delay of at most the communication time T before the state of a new output port of the controlling section 110 is transmitted to the controlled section 150. In other words, the time lag from the output of a control signal by the controlling section 110 to the arrival of the same signal at the controlled section 150 is 0 to the communication time T.
Thus, in engine ignition timing, for example, there will be a time lag of at most the communication time T between a target operation time and an actual operation time.